


In Love with My Best Friend's Brother

by SasuNaru_is_life



Category: Shingeki no Kyojin | Attack on Titan
Genre: Anal Fingering, Anal Sex, Armin Wears a Dress, Cheating, College Student Eren Yeager, Dirty Jokes, Dry Humping, FEMININE ARMIN, Flirty Eren Yeager, Fluff and Smut, Humor, M/M, Mikasa ships it, Nerd Armin Arlert, Older Eren Yeager, Piercings, Public Display of Affection, Punk Eren Yeager, Secret Relationship, Secrets, Tattooed Eren Yeager
Language: English
Status: Completed
Published: 2017-02-18
Updated: 2018-04-16
Packaged: 2018-09-25 09:53:23
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 9
Words: 5,698
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9814073
Author URL: https://archiveofourown.org/users/SasuNaru_is_life/pseuds/SasuNaru_is_life
Summary: Armin is in a happy relationship with Jean Kirstein until Eren Yeager comes around, Mikasa's older brother.





	1. Hypnotized

Armin knocked on Mikasa's door to see a totally handsome guy answer. The guy had brown hair, thickly shaped eyebrows, greenish blue eyes that could trap anybody within them, dimples that indent his cheeks, and a sharp jawline. He wore a black v neck long sleeve shirt, that clung to his firm chest, black sweatpants, and black socks. A skull rests on the side of his neck and piercings rest on his ears.

He found himself staring and blushing at the guy in front of him. "Like what you see?" he smiles, dimples poking out.

"I-I.........is Mikasa home?" Armin asked, clutching his book, and looking downwards.

"Answer my question first, sweetheart." The devil himself, gripping his chin, and smirking at him.

The blonde finds himself blushing. "Y-yes."

"Good boy." the guy grins, letting go of his chin. Armin loved the touch. "Yes, she is here. Come on in."

He stepped aside to let the blonde in. Armin sighs in relief when he sees Mikasa. That short moment with that stranger was torture. "Hey, Mikasa, and who's that by the way?"

She sighs. "That's Eren Yeager, my older brother."

Armin gasps. _One, her brother is extremely good looking. Two, he is such a flirt, and three, he is extremely good looking._ "For all these years I have known you, you have never told me you had an older brother."

"He was in living in a different country for all those years." Mikasa retorts.

The blonde looks behind himself to see Eren checking him out in his blue overalls, exposing his smooth legs, white crop, revealing his stomach, black rimmed glasses, and white converses. He blushes once again. The raven sees this unfold and pin points why Armin is turning red. _Oh, so he has a crush? I ship it._

"Now, that you know my name, what's yours, angel?" He asks, wrapping his arm around the blonde's waist, pulling him close to his body. Armin's face heats up once again.

"A-Armin Arlert." he stammers.

"What a beautiful name for such a beautiful boy." Eren whispers into his ear.

Mikasa coughs bringing both their attention onto her. She sighs and smiles at her older brother. "You do realize he has a boyfriend, right?"

Armin feels his heart start to break when he sees his pout. "I guess I will have to get rid of him."

The blonde covers his flustered face and escapes Eren's hold. The brunette laughs. "I guess I teased you enough, let me leave you guys alone."

Walking away, he whispers: "I wasn't joking about getting rid of your boyfriend. I want you all to myself."

* * *

Armin is so glad he escaped Mikasa's house. He can't handle Eren. He found himself falling in love with him, while he has Jean Kirschtein, his boyfriend. He tried to picture his Jean, and his hazel eyes, and all he thought about was Eren, Caribbean blues, dimples, well sculpted chest-

"Screw my life." the blonde facepalms.

 


	2. Left Alone with the Devil Himself

**Summary for the Chapter:**

> Mikasa leaves Armin alone with Eren. Which may or may not have been not such a smart decision.

Mikasa opened the door to see Armin, dressed in a white crop top hoodie, black skinny jeans, and white converse. He was carrying his Math textbook.  _As expected._

"Come on in, blondie." Mikasa smiled.

Armin grinned as he walked inside. He got used to coming to her house, it was like his second home. On the other hand, the blonde hasn't gotten used to Eren.

* * *

_Armin blushed as he felt a pair of vibrant green eyes on his ass. He was dressed in a blue tank top, white shorts that stopped mid thigh, and black combat boots. Why did Eren have to do this when Jean was here?_

_Of course, Jean was oblivious to the hungry looks that Armin was getting from Eren. He didn't notice how flustered the blonde got around him, how a gasp would leave him every time the brunette hugged his boyfriend. Armin couldn't get how Jean could hate someone so bad, and miss these obvious gestures._

_"I'm gonna go to the bathroom." Armin whispered, excusing himself._

_The blonde took a good look in the mirror, seeing his cheeks red, and how out of breath he was. Why did Eren had to be such an affect on the poor not._

_A few seconds later, Eren came in. Armin bit on his lip to stop himself from screaming. That damn devil! He knew the blonde was in the bathroom. Armin backed up against the counter. Eren put his hands on both sides of the counter, trapping him in._

_The brunette smirks as the flustered blonde checks him out in his black tank top, and black sweatpants. He watched how the blonde's gaze lingered on the tattoos._

_"E-Eren..what are you doing?" He stammered, meeting mischievous green eyes._

_"I can't check up on my favorite blonde?" He said in an innocent tone, lips latching onto pale skin._

_"Eren, my boyfriend is here! Please, stop!" Armin whined, hands latching onto the older male's shoulders._

_"We both know who you want more." Eren whispered, deep and husky into the blonde's ear._

_It was true, Armin did want Eren. He just didn't know how to get him without breaking Jean's heart._

_"Give yourself up to me, Arm. Forget about Jean." He growled, before leaving the bathroom, making Armin all hot and bothered._

* * *

Armin blushed, quickly getting rid of the memories. He sat down, making himself comfortable, until he saw Eren, in nothing but a towel.

His mouth hung open at the well sculpted chest, defined muscles and torso, and a towel blocking the sight of his possibly big cock.

The brunette smirks as he sees the blonde checking him out. He unraveled the towel a little, almost giving Armin a full peak.

"Like what you see, blondie?" He teased, making the blonde squirm.

Mikasa sighed as she watched the scene unfold. She could already tell Eren would be the end of Armin.

"Damn it, Eren. Go put some clothes on." Mikasa said with a hint of annoyance in her tone.

"Why should I? Armin is enjoying the view." The brunette grinned, flexing his muscles, making Armin squirm more.

"Eren. You have two seconds before I kick your ass." The raven warned.

"Oooh, scary." Eren mocked before going upstairs.

Armin wanted to scold Mikasa for getting rid of the brunette but he kept quiet. "Sorry about him."

"It's ok." Armin squeaks before properly adjusting his glasses.

After 20 minutes of homework, Mikasa remembered she had errands to run. Eren being "perfectly on time", came out dressed in black shorts with no shirt.  _Why, Eren, why? You should've just stayed naked._

"Damn it, Eren. I really don't trust leaving Armin alone with you." Mikasa scowled, scolding her older brother.

"What? You can trust me. Blondie and I are gonna have a great time." He grinned, slinging his arm around Armin's neck.

The blonde gave Mikasa a pleading look, one that said, "leave me alone with him, please!" and "don't leave me here."

Mikasa hesitantly trusted her brother. She left. Armin reached out a hand, wanting for her to take him, but it was too late. He slowly looked up at Eren, that gave him lust filled eyes.

Without giving the blonde a chance to speak, he pulled him onto his lap. Armin immediately stuck out his butt, wanting Eren to explore every part of him.

"I finally have you all to myself." He smirks, grabbing onto Armin's plump behind. A small moan leaves the blonde.

"No, Eren! We can't do this!" Armin yelled, having second guesses, trying to get himself out of Eren's strong hold.

"Yes, we can, and we will." Eren growled into the blonde's ear.

Armin couldn't stop his attraction to the brunette. His voice, his looks, and his body were seducing him to do the wrong thing.

Armin leaned over Eren's shoulder, sticking out his plump ass even more. The brunette began to slowly pull the blonde's skinny jeans down.

His eyes glimmer when he sees the white lace panties underneath the black skinny jeans.

"You're so perfect. How could such a horse get such a beautiful boy?" Eren complimented making Armin blush.

The brunette picked the blonde up, bridal style, carrying him to the bedroom. Once Armin was placed on the bed, Eren hurriedly removed all of the boy's clothes, not waiting any longer to be inside of Armin. He carefully took his glasses off though, not wanting them to be shattered.

The brunette admired the blonde's naked glory. His porcelain skin, pink nipples, long legs, curvy hips, basically his feminine figure as a whole.

Armin spread his legs, giving Eren a proper look. The brunette licks his lips, looking at the blonde's glistening hole made him hungry.

"Get ready, Armin. I'm gonna fuck you better than your horse boyfriend ever did." Eren growled, revealing his cock.

The blonde gasps. It was huge. Just by looking at it, Armin knew he was gonna be limping for days. Eren fully got rid of his shorts.

"Get on your knees, blondie." 

The blonde hurriedly complied, presenting for the brunette. A growl escaped Eren. Armin spread his ass cheeks apart, giving him a good look.

"Forget Jean, fill me with your cock, Eren. Leave me limping, making sure everyone knows that I belong to you." Armin moans.

The brunette was done for. He grabbed at Armin's hips and brutally thrusts in. The blonde cries out in pain. Eren stays in his position, making sure Armin is ok.

"Ah, it's ok! Please move, Eren." He says, gripping the sheets.

The brunette started thrusting at a slow pace, once Armin pushed back, trying to get him deeper, Eren picks up the pace. The blonde moans as he feels the older male nudging his stomach. Soon, they were moving at a compatible rhythm.

Eren found a spot that made Armin feel so good that he screamed. "PLEASE HIT IT AGAIN!"

He thrusted multiple times, hitting that spot. Armin jerked himself off, screaming as he finally came, ribbons of white coating the bed.

The older grabbed the blonde's hips harshly, abusing his insides, as he finally came deep inside. He pulled out, panting along with Armin.

_knock! Knock!_

 

Armin froze in shock, but not Eren. He smirked as he unlock the door, only showing his upper body. There was an angry Mikasa with her arms crossed. She gazed at her brother's undressed sweaty body. She gave Eren a questioning look.

"Hey Mika. Who knew fucking your best friend could be so good? His ass opens up easily for my cock." He grins mischievously, raking a hand through his sweaty hair.

Armin blushes embarrassingly as Eren tells Mikasa about how good he is in bed, totally giving away the fact they just had sex. 

"Fucking hell, Eren. I was dumb as shit for trusting your ass." Mikasa yells, stomping off.

 

 

 


	3. Update

**Summary for the Chapter:**

> Stop being lazy and read below.

Sorry guys, I haven't updated in a while, I am focusing on school. Teachers are giving a lot of homework. I will try to give an update by the end of this week.

 


	4. Party

**Summary for the Chapter:**

> Armin goes to Jean's party only to see the boy he has been trying to avoid.

"Remember Arm, party starts at 7." Jean says.

"Gotcha, babe." the blonde smiles, kissing his lover before walking in the direction of his house.

* * *

6:30 comes around quick. Armin takes a shower and comes out 10 minutes later. He quickly dries himself off. He puts on a white crop top sweater, black mid thigh shorts, and black converse. He leaves his glasses, knowing how wild Jean's parties can get. He grabs his phone and leaves.

"Need a ride to the party?" a familiar voice calls out. Armin turns around to see Connie and his girlfriend, Sasha inside their 2017 Hyundai Tucson.

"Thanks Connie." he smiles, getting inside the car.

"I hope there is lots of food there." Sasha squeals.

"Sasha, you are gonna turn into the Empire State Building if you keep that up." Connie says.

Armin starts dying of laughter. Sasha starts punching his arm. The laughter dies down when they reach Jean's house. The door's open and some people are drinking outside. Armin walks inside to find Jean wasted. "Arm, you f-finally made it!" he slurs.

"Yep, and you look like you are enjoying yourself." The blonde laughs before kissing his boyfriend.

"Even more that you are here." He whispers on his lips. Armin can practically taste the alcohol.

"HEY EREN! WELCOME TO THE PARTY!" someone screams.

The blonde immediately tenses up. He turns around to see the devil with a beanie, black tank, black ripped jeans, and black vans. Eren's eyes roam until he meets sapphire gems. He smirks, walking towards the boy.

"Jean, I am gonna go use the bathroom real quick." he excuses himself, trying to make a run for it, but Eren is too fast.

The brunette grabs his wrist, yanks him forward, making him hit his chest. Eren's other hand gently caresses Armin's waist. "Hey, cupcake." He smiles, making the blonde blush.

He shivers at the older male's warmth on his uncovered waist. "God, Eren. Why did you have to be here?"

"Why, trying to get rid of me?" Eren grins wide, dimples poking out. _Holy shit, can he get any hotter?_

"Yes, Eren. Now, please take your hands off me before Jean sees." Armin whines, trying to push Eren off. The brunette picks up on the sound and loves it.

"I don't want to. I love when my hands are on your body and I don't give a fuck if he sees. He can see me fucking you into oblivion." Eren whispers husky into his ear.

The blonde pants, grabbing onto his shoulders. Eren continues, "Would you like that, blondie? Want Jean to see how another man makes you feel so good?"

"N-No, Eren!" Armin whines, whole face turning red.

The brunette grabs onto his round ass, making the blonde shiver. Armin looks toward where Jean sat, and he sees him sleeping, getting carried upstairs by his friends. _There goes my plan of avoiding Eren._

"You should leave your glasses off more often. I love seeing the full beauty of your eyes." Eren compliments, nipping at his sensitive neck.

* * *

_To be continued.....  
_

 

 


	5. Party pt.2

**Summary for the Chapter:**

> Fucking read the story, you lazy hoes. Love yall.

Why did it have to turn out like this? Why did Eren have to come? I mean it's not like the brunette is pounding into Armin very aggressively on the matress. Mind you, this is in Jean's house, guest bedroom.

"Ah ah, E-Eren! You feel so good." The blonde moans looking up at the brunette.

His legs were on the older male's shoulders as his hole got abused. Eren was drenched in sweat, hair sticking to his forehead, muscles flex as he grips Armin's hips brutally.

"Look at how shameless you look fucking with another man in your boyfriend's house." Eren smirks devishly at Armin.

"S-shut up, you bastard." Armin curses for the first time, "This is all your fucking fault."

"Ooh, feisty." Eren mocks, "I like when your aggressive in bed as well."

"Damn it, Eren! Why did you have to exist? I wouldn't be cheating on my boyfriend! I wouldn't have fell in love with you, AHH!" The blonde curses as Eren finds his prostate.

The brunette grunts as he thrusts at a rapid pace into the blonde's hole. Armin finds himself stroking his length before spilling onto his chest. He layed motionless as Eren thrusted brutally into his entrance making slutty moans spill from Armin. He comes inside.

Pants fill the room. Eren whispers into the blonde's ear, "You know damn well you're glad you met me. Jean didn't fuck your little hole as good as I did. He didn't treat you with enough love as I did."

He hungrily nibbles on the blonde's ear lobe. Armin blushes, covering his flustered face. 

"Eren." Armin whines. Who knew that the blonde was still innocent and adorable after intense fucking and cursing?

Eren yanks away Armin's hands from his face so he can finally taste those pure lips. The blonde is shocked when the older male's lips meet his. He immediately wraps his arms around Eren's neck, bringing him in closer. 

He licks Armin's bottom lip. The blonde gladly opens his lips, giving Eren access to explore his mouth. He moans when the brunette's tongue explores his cavern.

Armin breaks the kiss to say, "I am glad that I met you."

* * *

 

Armin gives Jean a hug before leaving, drowning in the ocean of guilt. 


	6. Update

Hey guys. I haven't updated this story in a while, my bad. Now that I am back, and I would like an idea for the next chapter. I can't think of anything but having Jean find out and break up with Armin, but I want Eren and Armin's little scandal to go on a little further before Horsetein finds out....I mean Jean.

School is in 6 days for me. Pray for my soul. I hope you guys enjoy the rest of your summer because there is not much left of mine xD.


	7. Guilt

**Summary for the Chapter:**

> Armin stays home a whole week of school to contemplate things.

After Jean's party, Armin felt so much guilt. Yea, Eren is charming, hot, an ass, humorous, but definitely an ass, but was it really worth it? This is someone's feelings that he is hurting. He could never live with the guilt if Jean found out.

Armin went home. First thing he did was take off his clothes and take a shower, hoping to wash himself of all the sins he commited, and gain his purity back. He let the water travel down his body as he let his thoughts take over.

_You are a terrible person, Armin._

He lets out a sad laugh. "I know."

Once he gets out the shower, he uses one towel to dry his hair, and another towel to dry himself. He searches his closet for some comfortable clothes.

He finds a large hoodie, and a pair of short gym shorts. He slips them on, and jumps into his bed. He finds his phone and starts checking his notifications.

He got a message from a random number. He opens the text to see:

_From 9546789900:_

_Hey cupcake._

_................................_

_To 9546789900:_

_I am gonna take a huge guess and say this is from Eren._

_......................................_

_From 9546789900:_

_Bingo._

_......................................._

_To 9546789900:_

_When tf...no here's a better question, how tf did you get my number?_

_........................................_

_From 9546789900:_

_I know people_


	8. I know what I am going to do

**Summary for the Chapter:**

> Armin figures out his decision.

_To GreenEyedAsshole:_

_Don't play with me, who tf gave you my number?_

_................................................................._

_From GreenEyedAsshole:_

_Obviously, I went through Mikasa's phone while she was asleep and copied your contact into my phone._

_..........................................................................._

_To GreenEyedAsshole:_

_I hate your guts._

_............................................................................._

_From GreenEyedAsshole: No, you don't. You love everything about me_


	9. Made up my Mind

**Summary for the Chapter:**

> Armin calls it quits with Jean and he calls it on with Eren.
> 
>  
> 
> Ending

Armin doesn't have the courage to tell Jean to his face that he wants to break up. Breaking up through text is such an ass move, but he can't bear to see his reaction.

_To Jean:_

_I am sorry. I haven't been 100% truthful in our relationship. I have cheated, I have fell in love with another guy. I am such a bitch, I know. With time, I hope you will be able to forgive me. I hope we can be friends._

Armin smiles. He feels like huge weight has been lifted off his chest. Now, about Eren.

He puts on an oversized pink sweater and pink fur slides. He runs down the street. Eren is outside of the house in a grey flannel, black tank top, black jeans, and black vans.

"Eren!" He calls out.

"Hey cupcake, didn't get a text back from you last night? You ok?" He questions in concern.

"Yea, I was just thinking about things." Armin smiles, swinging his hands behind his back.

The brunette smirks as he grabs the blonde's waist. "I hope by "things" you mean us."

Armin blushes. "Yea. I called it quits with Jean. He deserves someone who will fully love him back. My heart wasn't being true to itself."

Eren smiles as he leans in. "Go on."

"My heart wants you, so I want to give you my heart if you let me." Armin smiles as he wraps his arms around the brunette's neck.

"Of course, and I will do the same by giving you my heart." 

Eren closes the space. He kisses Armin with love and passion. He finally got what he wanted. The blonde is all his. In return, he belongs to Armin.

Mikasa looks at the scene from a distance. A smile forms on her face. She knew it would be a thing. If only she bet money on it.

Armin breaks the kiss. "This seems like an ending to a Disney movie."

"It does, doesn't it?" Eren grins.

The brunette picks Armin up, bridal style. They turn around to see a happy Mikasa.

"Oh my shitballs, you two are so cute!!!"

"I know right." Eren winks at her.

"Well, I wanna celebrate. Celebrate the fact I can predict your futures. Who wants mint chocolate chip ice cream?"

Armin's eyes light up. "Oh hell yes!"

* * *

Meanwhile, Jean is shocked but not too mad. Ever since he started dating Armin, Marco started to look so much gorgeous to him. If Armin didn't cheat, he probably would've had.

In the end, everything worked out.

 

 

 


End file.
